const obj ={
  store:['foo','bar','baz'],
  [Symbol.iterator]:function () {
    let index = 0
    const self = this
    return {
      next:function () {  
        const result = {
          value:self.store[index],
          done:index>=self.store.length
        }
        index++
        return result
      }
      
    }
  }
}

for(const item of obj){
  console.log('循环体')
}